PROJECT SUMMARY/ABSTRACT Candidate. This K23 proposal will position Dr. Feig to become an independent investigator with expertise in developing and testing evidence-based interventions to improve health and well-being in patients with obesity. Her achievements thus far demonstrate her promise as a clinical researcher (20 publications, 20 presentations), and with additional training and mentorship she will significantly contribute to efforts to reduce the burden of obesity and improve quality of life for those with obesity. Mentorship. Mentors include experts in clinical trials and health behavior change (Drs. Huffman and Thorndike); qualitative research (Dr. Psaros), and medical and biological factors in obesity and weight-loss surgery (WLS; Drs. Kaplan and Thorndike). Collaborator Dr. Healy will provide biostatistical expertise and training, and consultant Dr. Lee will share her expertise in objective measurement of physical activity. Training Plan. Dr. Feig will achieve short-term goals through a research and training plan in (1) qualitative research; (2) designing and implementing trials for health behavior change interventions; and (3) physiological measures of health related to physical activity. Along with regular mentorship meetings and experiential training through the research plan, she will complete coursework, attend and present at seminars and national conferences, and publish findings in peer-reviewed journals. The training plan also includes courses and support programs specifically targeted at advancing her career as an independent investigator. Background. WLS is the most effective treatment available for severe obesity, yet about 25% of patients do not achieve sustained meaningful weight loss after surgery. Both adherence to health behaviors and psychological well-being are associated with weight loss maintenance after surgery. Access to ongoing support and intervention after surgery is often limited due to logistical barriers to regular clinic attendance. Accessible interventions are needed to improve adherence in post-WLS patients who are struggling. Research Strategy. To address this gap, the proposed study employs a mixed methods design to adapt and test a telehealth positive psychology-motivational interviewing (PP-MI) health behavior intervention to improve physical activity and psychological well-being in post-WLS patients from the Massachusetts General Hospital Weight Center. Phase 1 includes (1) qualitative interviews with post-WLS patients (n=20) to explore needs and intervention preferences. Phase 2 is a small single-arm pilot trial (n=10) of the newly adapted PP-MI intervention plus exit interviews, to further test and refine intervention content and study procedures. Phase 3 will entail a randomized controlled trial (n=50) to assess the feasibility and acceptability of the PP-MI intervention compared to an enhanced usual care control on physical activity and psychological well-being over 24 weeks. This K23 lays the groundwork for an R01 to assess efficacy in a full-scale trial.